An air-conditioning apparatus applicable to, for example, a multi-air-conditioning system for a building, is provided with a refrigerant circuit including an outdoor unit, which is a heat source unit disposed outside the building, and an indoor unit disposed inside the building that are connected with pipes. The air-conditioning apparatus circulates refrigerant through the refrigerant circuit to heat or cool air through radiation or reception of heat by the refrigerant, thereby heating or cooling the space to be air-conditioned.
Patent Literature 1 discloses an air-conditioning apparatus provided with an injection circuit including the injection ports of a bypass expansion device, a refrigerant heat exchanger, an on-off valve, and a compressor that are sequentially connected via an injection pipe branching from a fluid pipe connecting the refrigerant heat exchanger and the load-side expansion device. The air-conditioning apparatus injects the refrigerant under intermediate pressure during compression by the compressor, to increase the flow rate of the refrigerant. This configuration can maintain the heating capacity without an abnormal increase in the discharge temperature even at a low outdoor temperature.
Patent Literature 2 discloses a refrigerator including an intermediate injection flow channel that combines a portion of refrigerant flowing from a condenser to an evaporator with intermediate-pressure refrigerant in a compressor, and a suction injection flow channel that combines another portion of the refrigerant flowing from the condenser to the evaporator with low-pressure refrigerant sucked into the compressor. When the intermediate injection flow channel causes a reduction in operational efficiency in this refrigerator, the suction injection flow channel can reduce the discharge temperature of the compressor.